The 100m final at the Olympics: Lyles from last to first and the new photo-finish technology
This post shows why the men's 100m final at the Olympic Games was an uncommon race. Noah Lyles won the final despite being in last place for half of the time and the photo-finish was needed.
It’s Sunday 4th August at the Stade of France in Paris and eight sprinters are ready for the most important 10 seconds (a bit less) of the year. They know there is not a clear favorite like it was Usain Bolt and therefore each small detail can mark the difference between travelling back home with a medal or with a diploma.
The finalists also know that a 100m sprint is an extremely technical race in which a tiny detail can define the whole result and is divided in four phases, as Usain Bolt explains in the video below [1]. They are:
The start. The reaction time and the first two steps are really critical for most of the sprinters, especially in 60m sprints in indoor tracks. However, special athletes as Bolt can have average reaction times but later they recover the time loss.
Start - 30m. Called as drive phase, here the athlete has to keep the body forward and accelerate as much as possible, keeping the head a bit down.
30m - 50m. The athlete picks the knees up and the shoulders down, the head comes up and lifts the posture. This is the final acceleration.
50m - end. Usually at 50m the athletes reach their top speed, and in a 100m race ideally this speed would be maintained until the finish line. However, usually from 80m there is a small negative acceleration due to fatigue. Runners also must enter the finish line with the head in front, because the times are measured in the neck.
Not all sprinters are excellent in these four phase. Often the ones with better starts and lower reaction times have a slower top speed and the runners with slower starts have a higher top speed.
The race analysis
Lyles (USA) is the favorite because he is the current World Champion (Budapest 2023). His teammate Kerley is also really fast, as well the Jamaican Thompson. The Olympic champion in Tokyo, Jacobs (ITA) is not in as good physical form, but he is still a contender for the gold medal. Simbine (RSA) and Tebogo (BSW) are also strong, but Tebogo is more of a long sprint runner (200m - 400m).
After 9.79 seconds, Lyles won the race with the same time as Thompson. Kerley was third (9.81), Simbine fourth (9.82), Jacobs fifth (9.85) and Tebogo sixth (9.86). All the runners needed less than 10 seconds and it was the Olympic Final with less difference from the first to the last (9.78 vs 9.91) [2].
Lyles was the slowest runner in the start. With a bad reaction time, he was last in the first 10 meters, with 1.95 seconds time. Kerley and Jacobs had the best starts, with 1.87 seconds and Thompson needed 1.90 seconds. As shown in Fig. 1, when Jacobs (line 9 / bottom of the picture) and Kerley (line 3), Lyles (line 7) still had his left foot there.
However, Lyles was one of the faster athletes in the following phases. He was the fastest one in the last 20 meters, which was the key for the victory, as shows Fig. 2. We also see all the athletes reach maximum speed between 60m and 70m, except Kerley, the bronze medalist, who reached top speed between 50m and 60m. The best interval time was reached by Simbine, who only needed 0.81s to cover a 10m interval. Back to the Kerley different race pace, this is a common pattern in athletes with great start times. Another USA sprinter and 100m former World Champion, Coleman, has this same race pace, being the best athlete of the history of the 60m race.
This race was rare because there was a huge change of positions. In total, in only 100m, there were 20 overtakes. For example, in the feminine 100m final, Julien Alfred was first during the whole race.
The photo-finish technology
Given Thompson was first at 90m but Lyles came from behind, a photo-finish was needed to determine the champion. Even Thompson crossed first (his feet) the line, but the time is measured at the neck, and Lyles was faster in that.
Fig. 3. shows the picture OMEGA (the Olympic Games timekeeper) provided to the TV broadcasters. Everything is clear, but in fact it is not a picture [3]. The camera at the finish line takes continuous pictures (40000 frames per second) of the finish line and then all these frames are merged in a single picture and they add the advertisements on the top. Therefore, the photo-finish is built by the same points in different time instants. It is not a set of points at the same instant. This technique is called high-speed photography. The photo-finish technology used in previous Olympics could capture “only” 10000 frames per second.
References
[1] Usain Bolt describes the phases of the 100m sprint [Video] (kinetic-revolution.com)
[2] Men’s 100m final - Paris 2024 (olympics.com)
[3] How Omega Captured The Men's 100m Final Photo Finish (And The Watch Noah Lyles Wore While Winning) (hodinkee.com/articles/olympics-2024-mens-100m-photo-finish)